Initial experimental studies of electron accumulation in a heavy-ion beam

Abstract

Accelerators for heavy-ion inertial fusion energy (HIF) have an economic incentive to fit beam tubes tightly to beams, putting them at risk from electron clouds produced by emission of electrons and gas from walls. Theory and PIC simulations suggest that the electrons will be radially trapped in the ≥1 kV ion-beam potential. We are beginning studies on the High-Current Experiment (HCX) with unique capabilities to characterize electron production and trapping, the effects on ion beams, and mitigation techniques. We are measuring the flux of electrons and gas evolved from a target, whose angle to the beam can be varied between 78° and 88° from normal incidence. Quadrupole magnets are operating with a variety of internal charged particle diagnostics to measure the beam halo loss, net charge, electron ionization rate, and gas density.

US Heavy Ion Beam Research for High Energy Density Physics Applications and Fusion

“…These issues are being studied experimentally using a 1 MeV K + heavy ion beams [43] on the High Current Experiment (HCX), together with self-consistent numerical simulations and theoretical studies [44]. Electrons can be generated from three sources: ionization of residual gas; emission from the beam tube; and (in a linac) by emission from the end wall, each of which can be measured.…”

Energy loss, range, and electron yield comparisons of the CRANGE ion–material interaction code

“…These simulations are relevant to the High Current Experiment at Lawrence Berkeley National Laboratory [9]. Figure 1 shows simulation results for energy loss per unit length as a function of energy for both CRANGE and SRIM.…”

The High Current Transport Experiment for heavy-ion inertial fusion

“…Beam loss at the head and tail of the current pulse may be greater, and is presently being studied. The pickup signal due to lost ions is effectively amplified by the large secondary electron coefficient [3], making this diagnostic more sensitive to beam loss than comparisons of the total beam current data at the injector exit to that at QD1. The Faraday cupcurrent transformer ratio is >95(±2)%.…”

“…The Gas-Electron Source Diagnostic (GESD) is designed to measure the gas desorption and secondary electron and ion emission due to heavy-ion beams impacting a surface [3]. Approximately 0.1% of the beam current passes through a small aperture and strikes a target, adjustable between angles of incidence from 75 o to 88 o relative to normal.…”

“…A beam line of four pulsed magnetic quadrupoles, instrumented with diagnostics to measure the production and energy of trapped electrons, secondary atoms and ions was installed [3,8] downstream of the first group of 10 electrostatic quads in April 2003, and will be a principal area of activity in the next year.…”